1. Field of the Invention
The present invention relates to a single-wafer-processing type thin-film formation apparatus and method, which form a thin film on a workpiece, which is a semiconductor wafer, piece by piece.
2. Description of the Related Art
As thin-film formation apparatuses for thin film growth by atomic layer deposition, various types of formation apparatuses have been proposed. As typical examples, there are cases, in which gas is supplied from a gas-dispersion apparatus (i.e., a showerhead) disposed facing a substrate; and cases, in which gas is supplied by forming a laminar flow flowing in a direction from one edge of the substrate to the other edge without using the showerhead. In the case of a showerhead method, source gases can be supplied at uniform gas concentration onto the substrate surface, whereas in the case of a laminar-flow method, gas concentration in the upper stream tends to vary from gas concentration in the down stream. In the showerhead method, in order to supply gas onto the substrate surface uniformly, a source gas is stored inside the showerhead and is supplied onto the substrate using a dispersion plate having a relatively small conductance. For example, after a first gas is supplied, the remaining first gas is exhausted by supplying a second gas, and then a third gas is supplied; if the first gas still remains, solids are formed by a vapor chemical reaction. For this reason, when the third gas is supplied, it becomes necessary to sufficiently eliminate gases remaining in the dispersion apparatus. This conflicts with a primary feature of the showerhead, which stores gas inside it. Consequently, the showerhead method was considered that it was excellent in uniformity, but low in throughput, and other methods without using the showerhead method were more advantageous because exhausting reaction gases was easy.